PROJECT SUMMARY Musculoskeletal dysfunction and mobility impairments are a leading cause of disability in older adults, with shoulder pain identified as the 3rd most common musculoskeletal complaint. Shoulder pain can result in an inability to complete activities of daily living, increasing caretaker burden and long-term care needs in older adults. The mechanisms leading to degenerative shoulder pain and pathology are not precisely known, and remain a topic of ongoing debate and research. Altered muscle coordination has been implicated as a contributing factor to age-related shoulder pathology due to its direct influence on soft tissue loading. This proposal will focus on quantifying age-related changes in shoulder muscle activity to isolate changes in muscle coordination seen during healthy aging from those associated with pathology. Aim 1 will investigate shoulder muscle coordination during an isometric shoulder task, in which the coordination patterns of both voluntary muscle activity and involuntary responses to perturbations will be studied. Aim 2 will identify patterns of muscle coordination during dynamic reaching tasks to evaluate shoulder muscle activity during simulated activities of daily life. A muscle synergy analysis will be used to identify patterns of coordination from the rich data sets of muscle activity collected in these experiments. Age-related changes in muscle coordination patterns will be evaluated in healthy adults from 20-80 years old to isolate changes in coordination associated with healthy aging, and determine if altered muscle activity exists in the absence of pathology. The results of this work will provide essential normative data of shoulder muscle coordination across the lifespan, informing future studies aimed at identifying pre-clinical signs of pathology, developing preventative therapies, and minimizing the impact of age-related shoulder disability in older adults.